Use the Apple Hardware Test to Diagnose Problems

You can use the Apple Hardware Test (AHT) to diagnose issues you’re having with your Mac’s hardware. This can include problems with your Mac’s display, graphics, processor, memory, and storage. The Apple Hardware Test can be used to rule out most hardware failure as the culprit when you’re trying to troubleshoot problems you’re experiencing with your Mac.

Actual hardware failure is rare, but it does happen from time to time; the most common hardware failure is RAM.

The Apple Hardware Test can check your Mac’s RAM and let you know if there are any issues with it. With many Mac models, you can easily replace faulty RAM yourself, and save a few dollars in the process.

Which Macs Can Use the Internet-Based Apple Hardware Test?

Not all Macs can make use of the Internet-based AHT. Macs that are unable to use the Internet version of AHT can use a local version that’s either installed on the Mac’s startup drive or included on your OS X install DVD.

2013 and Later Macs

2013 and later Mac models make use of a newer version of the hardware test called Apple Diagnostics. You can find instruction for testing newer Macs using Apple Diagnostics at:

Note: Mid 2010 and early 2011 models may require an EFI firmware update before you can use Apple Hardware Test over the Internet. You can check to see if your Mac needs the EFI update by doing the following:

From the Apple menu, select About This Mac.

In the window that opens, click the More Info button.

If you’re running OS X Lion or later, click the System Report button; otherwise, continue with the next step.

In the window that opens, make sure Hardware is highlighted in the left-hand pane.

From the right-hand pane, make a note of the Boot ROM Version number, as well as the SMC Version number (if present).

With the version numbers in hand, go to the Apple EFI and SMC Firmware update website and compare your version against the latest available. If your Mac has an older version, you can download the latest version using the links on the above webpage.

Using the Apple Hardware Test Over the Internet

Now that you know your Mac is capable of using the AHT over the Internet, it’s time to actually run the test. To do this, you need either a wired or Wi-Fi connection to the Internet. If you have the required network connection, then let’s get started.

Make sure your Mac is turned off.

If you’re testing a Mac portable, be sure to connect it to an AC power source. Do not run the hardware test using only your Mac’s battery.

Press the power button to start the power on process.

Immediately hold down the Option and D keys.

Continue to hold the Option and D keys until you see a “Starting Internet Recovery” message on your Mac’s display. Once you see the message, you can release the Option and D keys.

After a short time, the display will ask you to “Choose Network.” Use the drop-down menu to make a selection from the available network connections.

If you chose a wireless network connection, enter the password and then press Enter or Return, or click the check mark button on the display.

Once you have connected to your network, you’ll see a message that says “Starting Internet Recovery.” This may take a while.

During this time, the Apple Hardware Test is being downloaded to your Mac. Once the download is complete, you will see the option to select a language.

Use the mouse cursor or the Up/Down arrow keys to highlight a language to use, and then click the button in the bottom right-hand corner (the one with the right-facing arrow).

The Apple Hardware Test will check to see what hardware is installed in your Mac. This process can take a little bit of time. Once it’s complete, the Test button will be highlighted.

Before you press the Test button, you can check what hardware the test found by clicking on the Hardware Profile tab. It’s a good idea to take a cursory look at the hardware profile, just to make sure that all of your Mac’s major components are showing up correctly. Be sure to verify that the correct amount of memory is being reported, along with the correct CPU and graphics. If anything appears to be wrong, you should verify what your Mac’s configuration should be. You can do this by checking Apple’s support site for the specifications on the Mac you are using. If the configuration information doesn’t match up, you may have a failed device that will need to be checked on.

If the configuration information appears to be correct, you can proceed to the testing.

Click the Hardware Test tab.

The Apple Hardware Test supports two types of testing: a standard test and an extended test. The extended test is a good option if you suspect an issue with your RAM or video/graphics. But even if you do suspect such a problem, it’s probably a good idea to start with the shorter, standard test.

Click the Test button.

The hardware test will start, displaying a status bar and any error messages that may result. The test can take a bit of time, so be patient. You may hear your Mac’s fans rev up and down; this is normal during the testing process.

When the test is complete, the status bar will disappear. The Test Results area of the window will display either a “No trouble found” message or a list of problems found. If you see an error in the test results, take a look at the error code section below for a list of common error codes and what they mean.

If no trouble was found, you may still want to run the extended test, which is better at finding memory and graphics problems. To run the extended test, place a check mark in the Perform Extended Testing (takes considerably more time) box, and then click the Test button.

Ending a Test in Process

You can stop any test in process by clicking the Stop Testing button.

Quitting the Apple Hardware Test

Once you finish using the Apple Hardware Test, you can quit the test by clicking either the Restart or Shut Down button.

Apple Hardware Test Error Codes

The error codes generated by the Apple Hardware Test tend to be cryptic at best, and are meant for Apple service technicians. Many of the error codes have become well known, however, and the following list should be helpful:

Apple Hardware Test Error Codes

Error Code

Description

4AIR

AirPort wireless card

4ETH

Ethernet

4HDD

Hard disk (includes SSD)

4IRP

Logic board

4MEM

Memory module (RAM)

4MHD

External disk

4MLB

Logic board controller

4MOT

Fans

4PRC

Processor

4SNS

Failed sensor

4YDC

Video/Graphics card

Most of the above error codes indicate a failure of the related component and may require having a technician look at your Mac, to determine the cause and the cost of a repair. But before you send your Mac off to a shop, try resetting the PRAM as well as resetting the SMC. This can be helpful for some errors, including logic board and fan problems.

You can perform additional troubleshooting for memory (RAM), hard disk, and external disk problems. In the case of a drive, whether internal or external, you can try repairing it using Disk Utility (which is included with OS X), or a third-party app, such as Drive Genius.

If your Mac has user-serviceable RAM modules, try cleaning and resetting the modules. Remove the RAM, use a clean pencil eraser to clean the RAM modules’ contacts, and then reinstall the RAM. Once the RAM is reinstalled, run the Apple Hardware Test again, using the extended testing option. If you still have memory issues, you may need to replace the RAM.

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